1. Field of the Invention
This invention relates to a luminescent material for an organic EL device having light-emitting properties.
2. Description of the Related Art
An organic electroluminescent device (organic EL device) is a light emitting device, containing a fluorescent material which emits light in response to the recombination of hole and electron injected from anode and cathode. For example, C. W. Tang et al. reported an organic EL device using a double-layered structure (Applied Physics Letters, 51,913 (1987)). This organic EL device, which has a tris (8-hydroxyquinolinol aluminum) in a light-emitting layer and a triphenyldiamine derivative in a hole-transporting layer, greatly enhances the luminescence properties.
To further improve luminescence efficiency, a method of doping a fluorescent dye had been utilized. For example, an organic EL device with a coumarin dye as the doping material (Applied Physics Letters, 65,3610 (1989)) has been used to greatly improve the luminescence efficiency. For improving the recombination efficiency of the injected hole and electron, multi-layered devices have been introduced. As a hole-transporting material, triphenylamine derivatives such as 4,4xe2x80x2,4xe2x80x3-tris(3-methylphenylphenylamino)-triphenylamine and aromatic diamine derivatives such as N,Nxe2x80x2-diphenyl-N,Nxe2x80x2 bis (3-methylphenyl)-[1,1xe2x80x2-biphenyl]-4,4xe2x80x2diamine are well known (see Japanese Patent Application Laid-Open Nos. 20771/1996, 40995/1996, 40997/1996, 53397/1996, 87122/1996). As an electron-transporting material, triazole derivatives and the like are also known.
Examples of the blue light emissive material for an organic EL device include condensed polycyclic aromatic compounds such as anthracene, pyrene and perylene (J. Chem. Phys., 44, 2902 (1996)), tetraphenylbutadiene-based compounds, distyrylbenzene-based compounds, stilbene-based compounds and polyphenyl-based compounds. (unexamined published Japanese patent application JP-A-61-37890, JP-A-1-245087, JP-A-2-247227, JP-A-2-247278, JP-A-2-209988, JP-A-3-33184, JP-A-3-84089, JP-A-3-231970, JP-A-4-117485, JP-A-4-275268, JP-A-5-17765, JP-A-140145, JP-A-3-47890, JP-A-3-33183, JP-A-5-247459 and JP-A-9-157642). However, these compounds have many problems involving durability, color purity, and luminescence efficiency.
An object of the present invention is to provide a high performance material and to provide an organic EL device having blue luminescence. The organic EL device comprises an anode, cathode, and one or more organic thin film layers which contain, either singly or as a mixture, an indole compound represented by the following formula (1), (2) or (3): 
wherein Y represents an extending aromatic group of the following general formula (4), (5) or (6): 
wherein Ar1 group represents a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group. X and Z represent a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted amino group, a substituted or unsubstituted alkoxy group a substituted or unsubstituted aryloxy group or a substituted or unsubstituted alkoxycarbonyl group; and Rx is one or more functional groups represented by a hydrogen atom, halogen atom, nitro group, cyano group, carboxyl group, or X. Two Rx groups may form a ring.